Final answer:
Small, nonpolar molecules like lipids, oxygen, carbon dioxide, and alcohol can easily diffuse through the lipid bilayer. Water-soluble materials like glucose, amino acids, and electrolytes need assistance to cross the membrane. Fat-soluble vitamins, drugs, and hormones can easily pass through the lipid core of the membrane.
Step-by-step explanation:
The lipid bilayer of the cell membrane allows only certain substances to pass through it unaided. Small, nonpolar molecules like lipids, oxygen, carbon dioxide, and alcohol can easily diffuse through the lipid bilayer. However, water-soluble materials like glucose, amino acids, and electrolytes need some assistance to cross the membrane because they are repelled by the hydrophobic tails of the phospholipid bilayer.
Additionally, lipid-soluble materials with a low molecular weight, such as the fat-soluble vitamins A, D, E, and K, can easily pass through the lipid core of the membrane. Fat-soluble drugs and hormones also gain easy entry into cells and are readily transported into the body's tissues and organs.
Molecules of oxygen and carbon dioxide have no charge and can pass through the membrane by simple diffusion.